In polymer melt spinning processes, polymer melt is supplied to a spinneret having numerous holes through which the melted polymer is extruded to form multiple polymer filaments which are drawn and taken up or wound onto a suitable means for receiving polymer filaments after the polymer filaments have been cooled. A quench fluid is directed across the path of the polymer filaments to cool them while they pass through a quench zone in the melt spinning process. Typically, the quench fluid is a quench air stream produced by chilling ambient air and blowing the quench air stream across the polymer filaments as they issue from the spinneret. For polymer filaments which are susceptible to degradation by contact with oxygen, inert fluids such as nitrogen may be used. The polymer filaments are protected from stray drafts by enclosing them in a protective chimney termed a quench zone or quench air cabinet until close to the point where the filaments converge to form a yarn or small tow.
Currently, several methods are used to set the quench fluid stream velocity in the quench zone of polymer melt spinning processes. One method involves two operators with a first operator measuring the quench fluid stream velocity with a hand held velometer and a second operator positioned at a quench fluid damper valve to make adjustments to the damper valve under direction of the first operator. Achieving accurate and reproducible quench fluid velocities using this method is cumbersome and time consuming, and operators must often shout above loud machinery noise. An even slower method involves a single operator who measures the quench fluid velocity and then adjusts the quench fluid damper valve. Through successive travels between the quench fluid damper valve and the velocity measurement location, with adjustments of the quench fluid damper valve, the desired quench fluid velocity is obtained. This method is time consuming especially if the damper valve and velocity measurement location are located on different floors of the polymer melt spinning process. Another method used for setting the quench fluid velocity is to measure the pressure behind the damper valve and to set the quench fluid velocity according to relative pressure drops. Clearly, for quick, accurate and repeatable setting of quench fluid velocities, the above methods are not acceptable.
U.S. Pat. No. 2,041,86 describes a means for stopping flow to a break or a serious leak in a fluid line by automative valves which may be opened and closed by manual control or remote control of a motor.
U.S. Pat. No. 2,662,547 describes an apparatus for automatically controlling the flow of air to the cabin of an aircraft in which the rotation of a butterfly valve is controlled by using a worm wheel sector and worm driven by a reversible motor.
U.S. Pat. No. 4,449,664 describes an air quantity regulating apparatus for air conditioning wherein an air quantity detector detects the quantity of air flowing through a duct member and delivers this information to a control mechanism to control a driving mechanism which uses a reversible driving motor, worm gear and worm wheel to drive a throttle valve which is intended to restrict the flow of air through the duct member.
The patents described above do not address polymer melt spinning processes or the need for quick, accurate and repeatable control of the quench fluid velocity used to cool the polymer filaments produced in the melt spinning process. Persons skilled in the art of melt spinning polymers would not look to these patents for a method and an apparatus for controlling a quench fluid stream velocity delivered to a quench zone in a polymer melt spinning process.
Many melt-spinning processes based on solid polymer resin melt the polymer resin with screw extruders fed directly with polymer in powdered or pellet form. A single extruder may supply several spinning positions through a series of branching pipes or tubes. The manifold leading from the extruder usually is designed in such a way as to minimize path lengths and differences in thermal history and residence time between the molten polymer supplied to the different spinning positions.
Many polyamide and polyester fiber plants are based upon continuous melt polymerization and in these plants the polymer is usually not solidified before spinning. Instead, the product is fed directly through a manifold from the polymerization plant to the spinning unit.
Whichever source of molten polymer is employed, the feed rate to individual spinning units is controlled by an accurately machined metering gear pump capable of feeding polymer against high back pressure and which delivers molten polymer at a constant rate into a filter assembly. The molten polymer is filtered through a series of sintered or fibrous metal gauzes or a bed of graded fine refractory material, such as sand or alumina, held in place by metal screens. Filtration removes large solid or gel particles that might otherwise block spinneret holes or, if passed through, occupy sufficient cross-sectional area in the polymer filament to affect its processing or tensile properties.
After filtration, the molten polymer passes to the spinneret through a short distribution system arranged to maximize mixing, equalize temperature, and minimize stagnancy. Dynamic mixers, static mixers, or flow inverters are sometimes included, for instance, in the manifold to improve the homogeneity of the molten polymer before the spinning positions.
Spinnerets for continuous-filament yarn production may have up to about 500 holes, most commonly 40 to 200, and those for tow may have several thousand. The holes and resulting filaments from a single continuous-filament spinning position may be divided into groups, e.g., a 50-hole spinneret may be used to produce two 25-filament yarns. As molten polymer passes through a spinneret hole, it is drawn and attenuated by a draw-down force applied by a windup roll or winder; simultaneously the temperature of the filaments rapidly decreases. The diameter of the polymer filament immediately below the spinneret hole and before attenuation begins is larger than the hole diameter. This phenomenon is termed die swell and is due to relaxation of the viscoelastic stress induced in the polymer filament as it is extruded through the spinneret hole. When spinning oxidation-sensitive polymers, it is useful to blanket a narrow zone immediately below the spinneret with inert gas in order to prevent deposition of degradation products around the orifices. A short cylindrical cowl, known as a shroud, extending downward for a short distance around the space immediately below the spinneret, maintains a blanket of hot gas around the nascent thread line and is used particularly where a spun yarn of low orientation but high orientability is required, as in the production of high tenacity yarns.
Immediately below this region, cool filtered air termed quench air is blown across the polymer filaments to promote uniform cooling. The quench air can be directed across the path of the filaments (crossflow quench), radially inward (inflow quench), or radially outward (outward quench).